Relaxational dynamics of polar nanodomains in Sr_{1 - x}Ca_xTiO₃, x = 0.002

The dielectric permittivity of Sr_{1 - x}Ca_xTiO₃, x - 0.002, measured at frequencies 10^-3 ≤ f ≤ 10⁷ Hz and temperatures 1.5 ≤ T ≤ 15 K, exhibits enhanced loss, ε″(f), on its low-f slope. This contrasts with conventional glassy dynamics and is attributed to dynamic heterogeneity involving thermally activated relaxation of dynamically coupled mesoscopic domains. Crossover into non-activated dynamics occurs at very low f as corroborated by temporal relaxation studies of the field-induced polarization P. Below T ≈ 3 K athermal quantum tunneling starts to dominate both ε″ (f) and P(t).